refactor(library/logic/core): use subscripts
refactor(library/logic/core): use subscripts

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

fgdorais/lean,dselsam/lean,avigad/lean,johoelzl/lean,johoelzl/lean,soonhokong/lean,leanprover-community/lean,leanprover/lean,eigengrau/lean,dselsam/lean,Kha/lean,rlewis1988/lean,fgdorais/lean,javra/lean,Kha/lean,javra/lean,johoelzl/lean,rlewis1988/lean,fpvandoorn/lean2,fgdorais/lean,soonhokong/lean-windows,soonhokong/lean-osx,eigengrau/lean,soonhokong/lean-windows,Kha/lean,htzh/lean,javra/lean,c-cube/lean,leanprover/lean,leanprover-community/lean,avigad/lean,leanprover/lean,soonhokong/lean-osx,levnach/lean,soonhokong/lean-osx,fgdorais/lean,rlewis1988/lean,UlrikBuchholtz/lean,rlewis1988/lean,leodemoura/lean,leodemoura/lean,digama0/lean,soonhokong/lean-osx,soonhokong/lean,fpvandoorn/lean,fpvandoorn/lean,soonhokong/lean-osx,eigengrau/lean,dselsam/lean,fpvandoorn/lean,johoelzl/lean,soonhokong/lean-windows,levnach/lean,leanprover-community/lean,digama0/lean,fpvandoorn/lean,c-cube/lean,htzh/lean,c-cube/lean,digama0/lean,c-cube/lean,soonhokong/lean,fpvandoorn/lean,Kha/lean,avigad/lean,soonhokong/lean-windows,levnach/lean,sp3ctum/lean,Kha/lean,fpvandoorn/lean2,digama0/lean,leodemoura/lean,leanprover-community/lean,fpvandoorn/lean,fpvandoorn/lean2,levnach/lean,dselsam/lean,leodemoura/lean,leanprover-community/lean,UlrikBuchholtz/lean,sp3ctum/lean,soonhokong/lean-windows,fgdorais/lean,c-cube/lean,eigengrau/lean,leanprover-community/lean,soonhokong/lean,fpvandoorn/lean2,javra/lean,sp3ctum/lean,leanprover/lean,htzh/lean,UlrikBuchholtz/lean,htzh/lean,sp3ctum/lean,johoelzl/lean,javra/lean,leanprover/lean,digama0/lean,rlewis1988/lean,fgdorais/lean,dselsam/lean,UlrikBuchholtz/lean,UlrikBuchholtz/lean,leodemoura/lean,leanprover/lean,levnach/lean,avigad/lean,fpvandoorn/lean2,johoelzl/lean,Kha/lean,eigengrau/lean,htzh/lean,soonhokong/lean,avigad/lean,digama0/lean,leodemoura/lean,rlewis1988/lean,sp3ctum/lean,avigad/lean,dselsam/lean